This invention relates to the art of fabricating universal joints, in particular, to the art of fabricating a means for suspending the rotor element of a gyroscope from a driving element or shaft.
One application for a universal joint for small angle deflections is found in the art of making free gyroscopes. A free gyroscope having a spinning rotor element may be mounted on a supporting structure so that the supporting structure can be turned or translated without applying disturbing torques to the rotor. In a practical device control torques are applied to the rotor element for processing the rotor element in a controlled manner. A free gyroscope customarily includes angular sensing devices for detecting angular misalignment between its rotor spin axis and either its shaft axis or a housing-fixed axis. The angular misalignment so detected may then be used, after appropriate amplification, to apply a torque to a supporting structure, such as a gimbal element of an inertial platform, to cause the supporting structure to follow the rotor spin axis thereby nulling the angular misalignment. Alternatively, a sensed angular misalignment may be utilized to apply a torque directly to the rotor element in what is known as "caged" or "captured" operation.
One of the ways a free gyroscope rotor element is maintained free is to support it by vibrating gimbal elements as disclosed in U.S. Pat. No. 3,678,764, issued July 25, 1972, and assigned to the same assignee as the present invention. The means for suspending the rotor element of that patent has separately fabricated gimbal elements and torsion bars with corresponding torsional axes angularly offset with respect to one another. U.S. Pat. No. 3,709,045 also discloses a two-piece suspension means with a pair of gimbal elements having corresponding torsional axes angularly offset from each other.
Other prior art patents teach the assembling, from separate pieces, of suspension means having a pair of gimbal elements in parallel alignment. Examples of patents teaching an inner hinge unit attached to an outer hinge unit are U.S. Pat. Nos. 3,354,726; 3,585,866; 3,614,894; 3,700,289; and 3,700,290. These prior art patents show two dissimilar gimbal elements attached to a shaft and to a rotor in a symmetrically parallel manner, i.e., the shaft-attached torsional axes of the gimbal elements aligned with respect to one another and the rotor attached torsional axes of the gimbal elements are aligned with respect to one another.
A flexure suspension having a single gimbal element is disclosed in U.S. Pat. No. 3,700,290.
Assembly of individual parts to form the flexure suspensions of the prior art requires extreme precision and adherence to close tolerances to fabricate a suspension unit having good performance characteristics. Misalignment of one or more axes of a flexure suspension used in a precision instrument such as a gyroscope will be a source of error in the performance of the gyroscope. Generally, assembly of the individual parts, for example by beam welding, brazing, etc. will cause some distortion to the parts during assembly and/or misalignment of the parts. For example, in flexure suspensions of the prior art it is difficult to achieve precisely a predetermined angle formed between corresponding flexure axes of multiple gimbal elements whether the angle is of zero degrees, of ninety degrees or has some other value. In addition, it is also difficult to achieve the desired result that each of the flexure axes of the gimbal elements precisely intersects all others at a common center point. Also, it is difficult to establish the center of gravity of a flexure suspension means precisely at the geometrical center of the suspension in both the radial and axial directions. Failure to achieve these alignments degrades performance characteristics and operating characteristics and degrades the accuracy of the instrument.
Additionally, the necessary precision alignment for a suspension formed or fabricated from separate parts requires extremely sophisticated fabricating and assembly equipment, and requires skilled personnel to perform the necessary alignment operations. Therefore it is desirable to fabricate a multigimbal flexure suspension from a single piece of material.